The present invention relates to solenoid operated valves of the type employing a spool type valving member which is moved by an operating rod connected to the armature of a solenoid. Valves of this type are often intended for proportional pressure control in response to a variable electrical signal. The invention particularly relates to the aforesaid proportional control valves of the type intended for operation from low voltage direct current power supplies as, for example, the 12 volt D.C. power supply provided on-board a motor vehicle.
Solenoid operated proportional control valves of the type operating from a vehicle power supply, are often employed for generating a hydraulic fluid pressure signal for shift control in an automatic transmission or other types of fluid operated actuators where precise control of the valve outlet pressure is required. In such applications, problems have been encountered with hysteresis and friction in the bearings supporting the operating rod and the armature. This has resulted in erratic valve performance and is imprecise or inadequate control of the pressure output in response to an electric control signal.
Heretofore, known solenoid operated pressure control valves have utilized an operating rod typically supported by a pair of bearings or bushings disposed in spaced relationship along the rod with a return spring bearing on the axial end of the armature for providing a bias in the desired operating direction e.g., either to the normally open or normally closed position depending upon the valve application.
However, the prior art valves as shown in FIG. 3 have employed the upper operating rod bearing or bushing denoted by reference numeral 1 disposed in the upper flux collector or pole piece 2 and a lower bearing 8 disposed in a lower flux collector 9 which is attached to the valve body. A return spring 3 is mounted axially outboard of the upper bearing 3; and, the preload of the spring adjusted by an adjustment member 4 threadedly engaging upper pole piece 2. This arrangement has encountered problems of hysteresis and misalignment of the operating rod and armature with respect to the conical working air gap 5 formed between the upper end of the armature and the lower end of the flux collector 2. Thus, it has been desired to provide a simple low cost way or means of reducing the hysteresis and improving the proportional control of a solenoid operated valve, particularly valves operated by low voltage direct current power supplies as found on board motor vehicles.